System and method for determining input from spatial position of an object

ABSTRACT

A system and method for determining an input is provided. The system includes an object position determination device and an input determination device. The object position determination device is configured to determine a first position of an object at a first time and a second position of the object at a second time. The object position determination device includes a camera configured to detect light traveling from the object to the camera. The input determination device is configured to determine an input based at least partly upon the first position and the second position. The object position determination device can include a second camera. The object can include a radio frequency emitter. The object can include an infrared emitter. The object can be an electronic device.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.11/225,726, entitled “A POINTING DEVICE AND CURSOR FOR USE ININTELLIGENT COMPUTING ENVIRONMENTS” and filed on Sep. 13, 2005, which isa divisional of U.S. patent application Ser. No. 10/461,646, entitled “APOINTING DEVICE AND CURSOR FOR USE IN INTELLIGENT COMPUTINGENVIRONMENTS” and filed on Jun. 13, 2003, the entire contents of each ofwhich are hereby incorporated by reference.

BACKGROUND

1. Technical Field

The application is related to determining input, and more particularlyto a system and process for determining input from the spatial positionof an object.

2. Background Art

Ubiquitous (i.e., intelligent) computing promises to blur the boundariesbetween traditional desktop computing and the everyday physical world. Apopular vision of tomorrow's computing pushes computational abilitiesinto everyday objects, each participating in a complex and powerfulintegrated intelligent environment. Tomorrow's home and officeenvironments, for example, may include a variety of small and largenetworked displays and smart controllable devices. For instance, themodern living room typically features a television, amplifier, DVDplayer, lights, computers, and so on. In the near future, these deviceswill become more inter-connected, more numerous and more specialized aspart of an increasingly complex and powerful integrated intelligentenvironment.

This migration away from the desktop and “into the walls” presentsseveral challenges for user interface design. For example, how does theuser of tomorrow's intelligent environment select one of many devices?Today, this problem is most often addressed by maintaining a separateinterface, such as an IR remote control, for each device.

Tomorrow's intelligent environment presents the opportunity to present asingle intelligent user interface (UI) to control many such devices whenthey are networked. This UI device should provide the user a naturalinteraction with intelligent environments. For example, people havebecome quite accustomed to pointing at a piece of electronic equipmentthat they want to control, owing to the extensive use of IR remotecontrols. It has become almost second nature for a person in a modernenvironment to point at the object he or she wants to control, even whenit is not necessary. Take the small radio frequency (RF) key fobs thatare used to lock and unlock most automobiles in the past few years as anexample. Inevitably, a driver will point the free end of the key fobtoward the car while pressing the lock or unlock button. This is doneeven though the driver could just have well pointed the fob away fromthe car, or even pressed the button while still in his or her pocket,owing to the RF nature of the device. Thus, a single UI device, which ispointed at electronic components or some extension thereof (e.g., a wallswitch to control lighting in a room) to control these components, wouldrepresent an example of the aforementioned natural interaction that isdesirable for such a device.

There are some so-called “universal” remote controls on the market thatare preprogrammed with the known control protocols of a litany ofelectronic components, or which are designed to learn the commandprotocol of an electronic component. Typically, such devices are limitedto one transmission scheme, such as IR or RF, and so can control onlyelectronic components operating on that scheme. However, it would bedesirable if the electronic components themselves were passive in thatthey do not have to receive and process commands from the UI devicedirectly, but would instead rely solely on control inputs from theaforementioned network. In this way, the UI device does not have todifferentiate among various electronic components, say by recognizingthe component in some manner and transmitting commands using someencoding scheme applicable only to that component, as is the case withexisting universal remote controls.

Of course, a common control protocol could be implemented such that allthe controllable electronic components within an environment use thesame control protocol and transmission scheme. However, this wouldrequire all the electronic components to be customized to the protocoland transmission scheme, or to be modified to recognize the protocol andscheme. This could add considerably to the cost of a “singleUI-controlled” environment. It would be much more desirable if the UIdevice could be used to control any networked group of new or existingelectronic components regardless of remote control protocols ortransmission schemes the components were intended to operate under.

It is noted that in the remainder of this specification, the descriptionrefers to various individual publications identified by a numericdesignator contained within a pair of brackets. For example, such areference may be identified by reciting, “reference [1]” or simply“[1]”. A listing of references including the publications correspondingto each designator can be found at the end of the Detailed Descriptionsection.

SUMMARY

In one embodiment, a system includes an object position determinationdevice and an input determination device. The object positiondetermination device is configured to determine a first position of anobject at a first time and a second position of the object at a secondtime. The object position determination device includes a cameraconfigured to detect light traveling from the object to the camera. Theinput determination device is configured to determine an input based atleast partly upon the first position and the second position. In anotherembodiment, the object position determination device includes a secondcamera.

In still another embodiment, the object includes a radio frequencyemitter. In yet another embodiment, the object includes an infraredemitter. In one embodiment, the object is an electronic device.

In one embodiment, a method includes detecting, by a camera, first lighttraveling from an object to the camera at a first time and determining afirst position of the object at the first time based at least partly onthe first light. The method also includes detecting, by the camera,second light traveling from the object to the camera at a second timeand determining a second position of the object at the second time basedat least partly on the second light. Further, the method includesdetermining an input based at least partly upon the first position andthe second position. In another embodiment, the method includesdetecting, by a second camera, third light traveling from the object tothe second camera at the first time, determining the first position ofthe object at the first time based at least partly on the third light,detecting, by the second camera, fourth light traveling from the objectto the second camera at the second time, and determining the secondposition of the object at the second time based at least partly on thefourth light. In yet another embodiment, the object includes a radiofrequency emitter. In still another embodiment, the object includes aninfrared emitter. In one embodiment, the object is an electronic device.

In one embodiment, a computer storage medium stores computer-executableinstructions that when executed by a processor cause a computer toexecute steps. The steps include detecting first light traveling from anobject to a camera at a first time and determining a first position ofthe object at the first time based at least partly on the first light.The steps also include detecting second light traveling from the objectto the camera at a second time and determining a second position of theobject at the second time based at least partly on the second light.Further, the steps include determining an input based at least partlyupon the first position and the second position. In another embodiment,the steps include detecting third light traveling from the object to asecond camera at the first time, determining the first position of theobject at the first time based at least partly on the third light,detecting fourth light traveling from the object to the second camera atthe second time, and determining the second position of the object atthe second time based at least partly on the fourth light. In yetanother embodiment, the object includes a radio frequency emitter. Instill another embodiment, the object includes an infrared emitter. Inone embodiment, the object is an electronic device.

DESCRIPTION OF THE DRAWINGS

The specific features, aspects, and advantages of various embodimentswill become better understood with regard to the following description,appended claims, and accompanying drawings where:

FIG. 1 is a diagram depicting a general purpose computing deviceconstituting an exemplary system for implementing various embodiments.

FIG. 2 is a diagram depicting a system for directing a laser beam withina space to act as a cursor according to one embodiment.

FIG. 3 is an image depicting one prototype version of the WorldCursordevice employed in the system of FIG. 2.

FIGS. 4A and B are a flow chart diagramming a process for modelingobjects in a space using the WorldCursor system of FIG. 2, wherein theobjects are modeled as circles using spherical coordinates.

FIGS. 5A and B are a flow chart diagramming a process for modelingobjects in a space using the WorldCursor system of FIG. 2, wherein theobjects are modeled as polygons using spherical coordinates.

FIG. 6 is a flow chart diagramming a process for automatically switchingbetween slow and fast filters to adjust the relative cursormovement-to-pointing device movement speed.

FIGS. 7A and B are a flow chart diagramming a clutching process foraligning the WorldCursor laser beam and XWand by making the laser beamshine on approximately the same location in the space that the XWand ispointed.

FIG. 8 is a flow chart diagramming one version of a process forestablishing and maintain a reasonable alignment between the pointingdevice and WorldCursor involving computing the 3D location of thepointing device and using this along with a knowledge of the rest of thegeometry of the space to compute the pitch and yaw angles that whenapplied to the WorldCursor laser will make it point at approximately thesame location as the pointing device.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

In the following description of the preferred embodiments, reference ismade to the accompanying drawings which form a part hereof, and in whichis shown by way of illustration specific embodiments. It is understoodthat other embodiments may be utilized and structural changes may bemade.

1.0 The Computing Environment

Before providing a description of the preferred embodiments, a brief,general description of a suitable computing environment in which variousembodiments may be implemented will be described. FIG. 1 illustrates anexample of a suitable computing system environment 100. The computingsystem environment 100 is only one example of a suitable computingenvironment and is not intended to suggest any limitation as to thescope of use or functionality of various embodiments. Neither should thecomputing environment 100 be interpreted as having any dependency orrequirement relating to any one or combination of components illustratedin the exemplary operating environment 100.

Various embodiments are operational with numerous other general purposeor special purpose computing system environments or configurations.Examples of well known computing systems, environments, and/orconfigurations that may be suitable for use with various embodimentsinclude, but are not limited to, personal computers, server computers,hand-held or laptop devices, multiprocessor systems,microprocessor-based systems, set top boxes, programmable consumerelectronics, network PCs, minicomputers, mainframe computers,distributed computing environments that include any of the above systemsor devices, and the like.

Various embodiments may be described in the general context ofcomputer-executable instructions, such as program modules, beingexecuted by a computer. Generally, program modules include routines,programs, objects, components, data structures, etc. that performparticular tasks or implement particular abstract data types. Variousembodiments may also be practiced in distributed computing environmentswhere tasks are performed by remote processing devices that are linkedthrough a communications network. In a distributed computingenvironment, program modules may be located in both local and remotecomputer storage media including memory storage devices.

With reference to FIG. 1, an exemplary system for implementing variousembodiments includes a general purpose computing device in the form of acomputer 110. Components of computer 110 may include, but are notlimited to, a processing unit 120, a system memory 130, and a system bus121 that couples various system components including the system memoryto the processing unit 120. The system bus 121 may be any of severaltypes of bus structures including a memory bus or memory controller, aperipheral bus, and a local bus using any of a variety of busarchitectures. By way of example, and not limitation, such architecturesinclude Industry Standard Architecture (ISA) bus, Micro ChannelArchitecture (MCA) bus, Enhanced ISA (EISA) bus, Video ElectronicsStandards Association (VESA) local bus, and Peripheral ComponentInterconnect (PCI) bus also known as Mezzanine bus.

Computer 110 typically includes a variety of computer readable media.Computer readable media can be any available media that can be accessedby computer 110 and includes both volatile and nonvolatile media,removable and non-removable media. By way of example, and notlimitation, computer readable media may comprise computer storage media.Computer storage media includes both volatile and nonvolatile, removableand non-removable media implemented in any method or technology forstorage of information such as computer readable instructions, datastructures, program modules or other data. Computer storage mediaincludes, but is not limited to, RAM, ROM, EEPROM, flash memory or othermemory technology, CD-ROM, digital versatile disks (DVD) or otheroptical disk storage, magnetic cassettes, magnetic tape, magnetic diskstorage or other magnetic storage devices, or any other medium which canbe used to store the desired information and which can be accessed bycomputer 110. Communication media typically embodies computer readableinstructions, data structures, program modules or other data in amodulated data signal such as a carrier wave or other transportmechanism and includes any information delivery media. The term“modulated data signal” means a signal that has one or more of itscharacteristics set or changed in such a manner as to encode informationin the signal. By way of example, and not limitation, communicationmedia includes wired media such as a wired network or direct-wiredconnection, and wireless media such as acoustic, RF, infrared and otherwireless media.

The system memory 130 includes computer storage media in the form ofvolatile and/or nonvolatile memory such as read only memory (ROM) 131and random access memory (RAM) 132. A basic input/output system 133(BIOS), containing the basic routines that help to transfer informationbetween elements within computer 110, such as during start-up, istypically stored in ROM 131. RAM 132 typically contains data and/orprogram modules that are immediately accessible to and/or presentlybeing operated on by processing unit 120. By way of example, and notlimitation, FIG. 1 illustrates operating system 134, applicationprograms 135, other program modules 136, and program data 137.

The computer 110 may also include other removable/non-removable,volatile/nonvolatile computer storage media. By way of example only,FIG. 1 illustrates a hard disk drive 141 that reads from or writes tonon-removable, nonvolatile magnetic media, a magnetic disk drive 151that reads from or writes to a removable, nonvolatile magnetic disk 152,and an optical disk drive 155 that reads from or writes to a removable,nonvolatile optical disk 156 such as a CD ROM or other optical media.Other removable/non-removable, volatile/nonvolatile computer storagemedia that can be used in the exemplary operating environment include,but are not limited to, magnetic tape cassettes, flash memory cards,digital versatile disks, digital video tape, solid state RAM, solidstate ROM, and the like. The hard disk drive 141 is typically connectedto the system bus 121 through an non-removable memory interface such asinterface 140, and magnetic disk drive 151 and optical disk drive 155are typically connected to the system bus 121 by a removable memoryinterface, such as interface 150.

The drives and their associated computer storage media discussed aboveand illustrated in FIG. 1, provide storage of computer readableinstructions, data structures, program modules and other data for thecomputer 110. In FIG. 1, for example, hard disk drive 141 is illustratedas storing operating system 144, application programs 145, other programmodules 146, and program data 147. Note that these components can eitherbe the same as or different from operating system 134, applicationprograms 135, other program modules 136, and program data 137. Operatingsystem 144, application programs 145, other program modules 146, andprogram data 147 are given different numbers here to illustrate that, ata minimum, they are different copies. A user may enter commands andinformation into the computer 110 through input devices such as akeyboard 162 and pointing device 161, commonly referred to as a mouse,trackball or touch pad. Other input devices (not shown) may include amicrophone, joystick, game pad, satellite dish, scanner, or the like.These and other input devices are often connected to the processing unit120 through a user input interface 160 that is coupled to the system bus121, but may be connected by other interface and bus structures, such asa parallel port, game port or a universal serial bus (USB). A monitor191 or other type of display device is also connected to the system bus121 via an interface, such as a video interface 190. In addition to themonitor, computers may also include other peripheral output devices suchas speakers 197 and printer 196, which may be connected through anoutput peripheral interface 195. Of particular significance to variousembodiments, a camera 163 (such as a digital/electronic still or videocamera, or film/photographic scanner) capable of capturing a sequence ofimages 164 can also be included as an input device to the personalcomputer 110. Further, while just one camera is depicted, multiplecameras could be included as input devices to the personal computer 110.The images 164 from the one or more cameras are input into the computer110 via an appropriate camera interface 165. This interface 165 isconnected to the system bus 121, thereby allowing the images to berouted to and stored in the RAM 132, or one of the other data storagedevices associated with the computer 110. However, it is noted thatimage data can be input into the computer 110 from any of theaforementioned computer-readable media as well, without requiring theuse of the camera 163.

The computer 110 may operate in a networked environment using logicalconnections to one or more remote computers, such as a remote computer180. The remote computer 180 may be a personal computer, a server, arouter, a network PC, a peer device or other common network node, andtypically includes many or all of the elements described above relativeto the computer 110, although only a memory storage device 181 has beenillustrated in FIG. 1. The logical connections depicted in FIG. 1include a local area network (LAN) 171 and a wide area network (WAN)173, but may also include other networks. Such networking environmentsare commonplace in offices, enterprise-wide computer networks, intranetsand the Internet.

When used in a LAN networking environment, the computer 110 is connectedto the LAN 171 through a network interface or adapter 170. When used ina WAN networking environment, the computer 110 typically includes amodem 172 or other means for establishing communications over the WAN173, such as the Internet. The modem 172, which may be internal orexternal, may be connected to the system bus 121 via the user inputinterface 160, or other appropriate mechanism. In a networkedenvironment, program modules depicted relative to the computer 110, orportions thereof, may be stored in the remote memory storage device. Byway of example, and not limitation, FIG. 1 illustrates remoteapplication programs 185 as residing on memory device 181. It will beappreciated that the network connections shown are exemplary and othermeans of establishing a communications link between the computers may beused.

The exemplary operating environment having now been discussed, theremaining part of this description section will be devoted to adescription of the program modules embodying various embodiments.

2.0 The XWand System

In a co-pending U.S. patent application entitled “A SYSTEM AND PROCESSFOR SELECTING OBJECTS IN A UBIQUITOUS COMPUTING ENVIRONMENT” which wasfiled on May 31, 2002 and issued Ser. No. 10/160,692, a system andprocess was introduced that provides a remote control UI device that iscapable of controlling a group of networked electronic components. Moreparticularly, the UI device, which will herein be referred to as theXWand, is able to control the electronic components without having todirectly differentiate among the components or employ a myriad ofdifferent control protocols and transmission schemes. And in order toprovide a natural interaction experience, the present system is operatedby having the user point at the electronic component (or an extensionthereof) that he or she wishes to control. In particular, the XWandprovides a remote control UI device that can be simply pointed atobjects in an ubiquitous computing environment that are associated insome way with controllable, networked electronic components, so as toselect that object for controlling via the network. This can for exampleinvolve pointing the UI device at a wall switch and pressing a button onthe device to turn a light operated by the switch on or off. The idea isto have a UI device so simple that it requires no particular instructionor special knowledge on the part of the user.

The XWand system includes the aforementioned remote control UI device inthe form of a wireless RF pointer, which includes a radio frequency (RF)transceiver and various orientation sensors. The outputs of the sensorsare periodically packaged as orientation messages and transmitted usingthe RF transceiver to a base station, which also has a RF transceiver toreceive the orientation messages transmitted by the pointer. There isalso a pair of digital video cameras each of which is located so as tocapture images of the environment in which the pointer is operating fromdifferent viewpoints. A computer, such as a PC, is connected to the basestation and the video cameras. Orientation messages received by the basestation from the pointer are forwarded to the computer, as are imagescaptured by the video cameras. The computer is employed to compute theorientation and location of the pointer using the orientation messagesand captured images. The orientation and location of the pointer is inturn used to determine if the pointer is being pointed at an object inthe environment that is controllable by the computer via a networkconnection. If it is, the object is selected.

The pointer specifically includes a case having a shape with a definedpointing end, a microcontroller, the aforementioned RF transceiver andorientation sensors which are connected to the microcontroller, and apower supply (e.g., batteries) for powering these electronic components.In the tested versions of the pointer, the orientation sensors includedat least, an accelerometer that provides separate x-axis and y-axisorientation signals, and a magnetometer that provides separate x-axis,y-axis and z-axis orientation signals. These electronics were housed ina case that resembled a wand-hence the XWand name.

The pointer's microcontroller packages and transmits orientationmessages at a prescribed rate. While the microcontroller could beprogrammed to accomplish this task by itself, a command-responseprotocol was employed in tested versions of the system. This entailedthe computer periodically instructing the pointer's microcontroller topackage and transmit an orientation message by causing the base stationto transmit a request for the message to the pointer at the prescribedrate. This prescribed rate could for example be approximately 50 timesper second as it was in tested versions of the system.

As indicated previously, the orientation messages generated by thepointer include the outputs of the sensors. To this end, the pointer'smicrocontroller periodically reads and stores the outputs of theorientation sensors. Whenever a request for an orientation message isreceived (or it is time to generate such a message if the pointer isprogrammed to do so without a request), the microcontroller includes thelast-read outputs from the accelerometer and magnetometer in theorientation message.

The pointer also includes other electronic components such as a useractivated switch or button, and a series of light emitting diodes(LEDs). The user-activated switch, which is also connected to themicrocontroller, is employed for the purpose of instructing the computerto implement a particular function. To this end, the state of the switchin regard to whether it is activated or deactivated at the time anorientation message is packaged is included in that message fortransmission to the computer. The series of LEDs includes a pair ofdifferently-colored, visible spectrum LEDs, which are connected to themicrocontroller, and which are visible from the outside of the pointer'scase when lit. These LEDs are used to provide status or feedbackinformation to the user, and are controlled via instructions transmittedto the pointer by the computer.

The foregoing system is used to select an object by having the usersimply point to the object with the pointer. This entails the computerfirst inputting the orientation messages transmitted by the pointer. Foreach message received, the computer derives the orientation of thepointer in relation to a predefined coordinate system of the environmentin which the pointer is operating using the orientation sensor readingscontained in the message. In addition, the video output from the videocameras is used to ascertain the location of the pointer at a timesubstantially contemporaneous with the generation of the orientationmessage and in terms of the predefined coordinate system. Once theorientation and location of the pointer are computed, they are used todetermine whether the pointer is being pointed at an object in theenvironment that is controllable by the computer. If so, then thatobject is selected for future control actions.

The computer derives the orientation of the pointer from the orientationsensor readings contained in the orientation message as follows. First,the accelerometer and magnetometer output values contained in theorientation message are normalized. Angles defining the pitch of thepointer about the x-axis and the roll of the device about the y-axis arecomputed from the normalized outputs of the accelerometer. Thenormalized magnetometer output values are then refined using these pitchand roll angles. Next, previously established correction factors foreach axis of the magnetometer, which relate the magnetometer outputs tothe predefined coordinate system of the environment, are applied to theassociated refined and normalized outputs of the magnetometer. The yawangle of the pointer about the z axis is computed using the refinedmagnetometer output values. The computed pitch, roll and yaw angles arethen tentatively designated as defining the orientation of the pointerat the time the orientation message was generated. It is next determinedwhether the pointer was in a right-side up or up-side down position atthe time the orientation message was generated. If the pointer was inthe right-side up position, the previously computed pitch, roll and yawangles are designated as the defining the finalized orientation of thepointer. However, if it is determined that the pointer was in theup-side down position at the time the orientation message was generated,the tentatively designated roll angle is corrected accordingly, and thenthe pitch, yaw and modified roll angle are designated as defining thefinalized orientation of the pointer. In the foregoing description, itis assumed that the accelerometer and magnetometer of the pointer areoriented such that their respective first axis corresponds to the x-axiswhich is directed laterally to a pointing axis of the pointer and theirrespective second axis corresponds to the y-axis which is directed alongthe pointing axis of the pointer, and the third axis of the magnetometercorrespond to the z-axis which is directed vertically upward when thepointer is positioned right-side up with the x and y axes lying in ahorizontal plane.

The computer derives the location of the pointer from the video outputof the video cameras as follows. There is an infrared (IR) LED connectedto the microcontroller that is able to emit IR light outside thepointer's case when lit. The microcontroller causes the IR LEDs toflash. In addition, the aforementioned pair of digital video cameraseach have an IR pass filter that results in the video image framescapturing only IR light emitted or reflected in the environment towardthe camera, including the flashing from the pointer's IR LED whichappears as a bright spot in the video image frames. The microcontrollercauses the IR LED to flash at a prescribed rate that is approximatelyone-half the frame rate of the video cameras. This results in only oneof each pair of image frames produced by a camera having the IR LEDflashes depicted in it. This allows each pair of frames produced by acamera to be subtracted to produce a difference image, which depicts forthe most part only the IR emissions and reflections directed toward thecamera which appear in one or the other of the pair of frames but notboth (such as the flash from the IR LED of the pointing device). In thisway, the background IR in the environment is attenuated and the IR flashbecomes the predominant feature in the difference image. The imagecoordinates of the pixel in the difference image that exhibits thehighest intensity is then identified using a standard peak detectionprocedure. A conventional stereo image technique is then employed tocompute the 3D coordinates of the flash for each set of approximatelycontemporaneous pairs of image frames generated by the pair of camerasusing the image coordinates of the flash from the associated differenceimages and predetermined intrinsic and extrinsic camera parameters.These coordinates represent the location of the pointer (as representedby the location of the IR LED) at the time the video image frames usedto compute them were generated by the cameras.

The orientation and location of the pointing device at any given time isused to determine whether the pointing device is being pointed at anobject in the environment that is controllable by the computer. In orderto do so the computer must know what objects are controllable and wherethey exist in the environment. This requires a model of the environment.In the XWand system, the location and extent of objects within theenvironment that are controllable by the computer are modeled using 3DGaussian blobs defined by a location of the mean of the blob in terms ofits environmental coordinates and a covariance. Two different methodshave been developed to model objects in the environment.

The first involves the user inputting information identifying the objectthat is to be modeled. The user then activates the switch on thepointing device and traces the outline of the object. Meanwhile, thecomputer is running a target training procedure that causes requests fororientation messages to be sent to the pointing device a prescribedrequest rate. The orientation messages are input as they are received,and for each orientation message, it is determined whether the switchstate indicator included in the orientation message indicates that theswitch is activated. Whenever it is initially determined that the switchis not activated, the switch state determination action is repeated foreach subsequent orientation message received until an orientationmessage is received which indicates that the switch is activated. Atthat point, each time it is determined that the switch is activated, thelocation of the pointing device is ascertained as described previouslyusing the digital video input from the pair of video cameras. When theuser is done tracing the outline of the object being modeled, he or shedeactivates the switch. The target training process sees this as theswitch has been deactivated after having been activated in theimmediately preceding orientation message. Whenever such a conditionoccurs, the tracing procedure is deemed to be complete and a 3D Gaussianblob representing the object is established using the previouslyascertained pointing device locations stored during the tracingprocedure.

The second method of modeling objects once again begins by the userinputting information identifying the object that is to be modeled.However, in this case the user repeatedly points the pointer at theobject and momentarily activates the switch on the device, each timepointing the device from a different location within the environment.Meanwhile, the computer is running a target training procedure thatcauses requests for orientation messages to be sent to the pointingdevice at a prescribed request rate. Each orientation message receivedfrom the pointing device is input until the user indicates the targettraining inputs are complete. For each orientation message input, it isdetermined whether the switch state indicator contained thereinindicates that the switch is activated. Whenever it is determined thatthe switch is activated, the orientation of the pointing device iscomputed as described previously using orientation sensor readings alsoincluded in the orientation message. In addition, the location of thepointing device is ascertained using the inputted digital video from thepair of video cameras. The computed orientation and location values arestored. Once the user indicates the target training inputs are complete,the location of the mean of a 3D Gaussian blob that will be used torepresent the object being modeled is computed from the pointingdevice's stored orientation and location values. The covariance of theGaussian blob is then obtained in one of various ways. For example, itcan be a prescribed covariance, a user input covariance, or thecovariance can be computed by adding a minimum covariance to the spreadof the intersection points of rays defined by the pointing device'sstored orientation and location values.

With a Gaussian blob model of the environment in place, the orientationand location of the pointing device can be is used to determine whetherthe pointing device is being pointed at an object in the environmentthat is controllable by the computer. In one version of this procedure,for each Gaussian blob in the model, the blob is projected onto a planewhich is normal to either a line extending from the location of thepointing device to the mean of the blob or a ray originating at thelocation of the pointing device and extending in a direction defined bythe orientation of the device. The value of the resulting projectedGaussian blob at a point where the ray intersects the plane is computed.This value represents the probability that the pointing device ispointing at the object associated with the blob under consideration.Next, the probability representing the largest value computed for theGaussian blobs, if any, is identified. At this point, the objectassociated with the Gaussian blob from which the largest probabilityvalue was derived could be designated as being the object that thepointing device is pointing at. However, an alternate thresholdingprocedure could be employed instead. In this alternate version, it isfirst determined whether the probability value identified as the largestexceeds a prescribed minimum probability threshold. Only if thethreshold is exceeded is the object associated with the projectedGaussian blob from which the largest probability value was deriveddesignated as being the object that the pointer is pointing at. Theminimum probability threshold is chosen to ensure the user is actuallypointing at the object and not just near the object without an intent toselect it.

In an alternate procedure for determining whether the pointing device isbeing pointed at an object in the environment that is controllable bythe computer, for each Gaussian blob, it is determined whether a rayoriginating at the location of the pointing device and extending in adirection defined by the orientation of the device intersects the blob.Next, for each Gaussian blob intersected by the ray, it is determinedwhat the value of the Gaussian blob is at a point along the ray nearestthe location of the mean of the blob. This value represents theprobability that the pointing device is pointing at the objectassociated with the Gaussian blob. The rest of the procedure is similarto the first method in that the object associated with the Gaussian blobfrom which the largest probability value was derived could be designatedas being the object that the pointing device is pointing at. Oralternately, it is first determined whether the probability valueidentified as the largest exceeds the prescribed minimum probabilitythreshold. If the threshold is exceeded, only then is the objectassociated with the projected Gaussian blob from which the largestprobability value was derived designated as being the object that thepointing device is pointing at.

Users of the XWand are often impressed with the immediate and naturalfeel of absolute pointing. However, the pure geometry-based approachwhich enables absolute pointing also has a number of importantdrawbacks. First, two or more cameras must be permanently mounted in theroom. Besides the difficulty of installation, such cameras inevitablydraw objections related to privacy. In addition, the cameras must becarefully calibrated to the room geometry upon installation, andrecalibrated if they are moved. Further, at least two cameras must haveclear sight-lines to the wand at all times. Finally, the threedimensional position of each active device in the room must be known,and small errors in the orientation and position information translateto inaccuracy in pointing, possibly disrupting the interaction.

Given these objections, alternatives to absolute pointing would beadvantageous with the goal of eliminating the three dimensionalpositioning system. One general approach is to place tags in theenvironment, but they have drawbacks as well. By design tags requireinstallation on every active device. Active tags such as IR beacons, forexample, require their own power, while passive tags such as RF ID tagstend to have limited range, and tags based on visual features rely onrather sophisticated onboard processing.

3.0 WorldCursor System

The foregoing XWand system issues are resolved by the present system,which will be referred to herein as the WorldCursor system. TheWorldCursor system uses the XWand device (or similar pointing device)but does not rely on a geometric model of pointing that requires thethree dimensional position of the XWand, nor on tags placed in theenvironment, nor on any external sensing in general. Instead, a laserbeam projected in the space gives the user feedback as to where thesystem believes the user is pointing, much in the same way that thecursor icon in “windows, icons, menus and pointing” (WIMP) interfacesprovides feedback to indicate where the user is pointing with the mouse.In fact, the WorldCursor is analogous to the mouse and cursor used intraditional GUIs in that the user may select and interact with aphysical device by positioning the cursor on the device and clicking.

In the foregoing context, the XWand is employed as a physical pointingmechanism, and it is coupled with the WorldCursor which projects acursor on the physical environment. The WorldCursor improves upon theXWand by removing the need for external positioning technology such asvideo cameras or any other external position sensing technology, and byenabling the user to point with a high degree of precision.

Referring to FIG. 2, the WorldCursor system includes a smalltele-operated motion platform 200 upon which is mounted a laser pointer.This device is controlled via a wired connection 202 to a host computer204, which is also connected to the XWand RF base station 206. TheWorldCursor platform 200 can be programmed to follow the motion of theXWand 208, such that when the user points the XWand to the left, forexample, the WorldCursor moves a corresponding amount to the left inreal time. The user attends to the projected laser spot (the cursor) inthe environment. By moving the XWand the user is then able to place thecursor on any object in the room, as they would place the cursor on anonscreen object with the mouse. Because only the orientation informationfrom the XWand is used, and not the XWand's 3-D position, the originalXWand system's requirement of the external computer vision system iseliminated.

Interacting with active devices in the intelligent environment proceedsmuch as in the original XWand system. For example, to turn a householdlamp on or off, instead of pointing directly at the lamp, the user movesthe laser spot onto the lamp and clicks the XWand button. The systemdetermines that the cursor is on the lamp by comparing the currentcursor position with the recorded cursor position associated with thelamp, collected beforehand.

3.1 The WorldCursor Device

In general, the WorldCursor device simply needs to take yaw and pitchcommands in some form and in response move the laser spot to any desiredplace (within line of sight of the laser) in the space in which it isoperating. Any device having this capability will suffice for use in theoverall WorldCursor system. In tested embodiments of the WorldCursorsystem the aforementioned device took the form of a motion platform thatis mounted on the ceiling, typically near the center of the room. Aprototype of this device is shown in FIG. 3. It consisted of two highspeed miniature servos, such as the type used on radio-controlled modelairplanes. Specifically, in tested embodiments of the WorldCursor,Expert Electronic's SL451 High Speed Mini Servos (Model EXRSL451) wereused. One of the servos was mounted for yaw and a second for pitchcontrol. In one embodiment of the device, both servos were controlled bya PIC microcontroller, which takes yaw and pitch commands from the hostcomputer via a RS-232 connection and converted them to standard servomotor commands. In an alternate embodiment, an API on the aforementionedhost computer takes yaw and pitch values from the XWand, and convertsthen to standard servo motor commands. These commands are then sent tothe servos. It is noted that this latter scenario has the advantage ofsending motor commands that are typically in integer form, rather thanfloating point data such as would be the case with pitch and yaw values.

Mounted on the servo assembly is a red laser similar to those used inconventional laser pointers. By controlling the servos, the platform isable to steer the laser spot to most points in the room below theceiling, provided there exists a sight line to that point. In testedversions of the present system and process, effective resolution insteering the laser using the aforementioned servos is about 0.25 degreesor about one half inch at a distance of 9 feet. The servos were eachcapable of moving over nearly a 170 degree range at a speed of 333degrees per second. Generally, this configuration resulted in the motionof the laser being smooth and responsive. However, in the case when thelaser must move from pointing to a location in front of the platform toa location behind the platform, the pitch motor must move to the backand the yaw motor must reflect about the vertical plane separating thefront and rear hemispheres. Because the servos employed in the testedembodiments had a 170 degree range limitation, there was a discontinuityin this movement of the laser spot from front to back (i.e., a 20 degreegap at the sides). While the aforementioned pointing inaccuracy anddiscontinuity were not found to be a problem in the tested embodiments,ideally, servos with a full 180 degree range and higher accuracy couldbe employed to resolve these minor deficiencies.

It is noted that the connection between the WorldCursor base unit andthe host computer could also be of a wireless type. However, if this isthe case care must be taken to ensure there is no interference with theXWand system.

3.2 World Model for the WorldCursor System

The WorldCursor points at a given object in the room by changing thepitch and yaw of the laser with its motors. It is therefore possible touniquely associate a given object in the room with the yaw and pitchvalue used to point the WorldCursor at the object. The yaw and pitchvalues of each object of interest in the space are the basis for aconvenient world model for the WorldCursor system based on sphericalcoordinates.

The spherical coordinate world model is easier to construct than thefull three dimensional model of the original XWand system as describedpreviously. For example, whereas in the three dimensional model the userhad to either hold the XWand over the object, or provide severalpointing examples used to triangulate the position of the object, theWorldCursor system need only record the current yaw and pitch values ofthe device once the user has put the cursor on the object. Onelimitation of this approach is that the spherical coordinate world modelmust be re-learned if the WorldCursor device is moved to a new location.

Given this, a model of the space that the WorldCursor system is tooperate in can be established as follows. Referring to FIGS. 4A and B,the user initiates a training mode that is part of a WorldCursor controlprocess running on the host computer (process action 400). The trainingmode has the same purpose as a similar process used in the XWandsystem—namely to learn where objects of interest are in the space. Moreparticularly, the user directs the laser at an object of interest bypointing the XWand so that the laser spot appears on the approximatecenter of the object being modeled and presses the button on the XWand(process action 402). The control process causes periodic requests to besent to the XWand directing it to provide an orientation message in themanner described previously (process action 404). Any incomingorientation message transmitted by the pointer is input (process action406), and it is determined whether the button state indicator includedin the message indicates that the pointer's button is activated (processaction 408). If not, process actions 406 and 408 are repeated. When itis discovered that the button state indicator indicates the button isactivated, then in process action 412, the control process accepts inputfrom the user who enters information into the host computer thatidentifies the object being modeled, including its approximate size(process action 410). Since it was the control process running on thehost computer that received the pitch and yaw data from the XWand andmoved the laser of the WorldCursor to the target location as describedpreviously, the pitch and yaw associated with the target spot are known.The process associates the spherical coordinates of the target locationto the information entered by the user about the corresponding object(process action 414). In addition, the user-provided size data is usedto establish a circle in spherical coordinates about the direction thelaser is pointed that models the extent of the object (process action416). Any incoming orientation message transmitted by the pointercontinues to be input (process action 418) and a determination is madeas to whether the button state indicator included in the messages firstindicates that the pointer's button becomes deactivated and thenactivated again, thereby indicating that the user has pushed the XWandbutton again (process action 420). If it is, process actions 418 and 420are repeated. If it is not, in process action 424, it is determined ifthe user has deactivated the training mode (process action 422), thusindicating all the objects it is desired to model in the space have beenmodeled. If the user has not deactivated the training mode, then processactions 402 through 424 are repeated to “learn” the next object the userchooses to identify to the system. Otherwise the process ends.

Once the objects in the space have been modeled as described above, usercan direct the laser of the WorldCursor to the modeled objects and actupon them as was done in the XWand system. More particularly, the usershines the WorldCursor's laser beam on the object he or she wants toselect. It is then determined whether the laser beam is on an object inthe space that is known. Whenever the laser beam is on a known object,that object is selected for future control actions.

To determine if the laser beam is on an object, the user is required toactivate the XWand switch when the laser beam is shining on the objecthe or she wants to select. The distance is computed in sphericalcoordinates between the current WorldCursor position and a positionstored for each of the modeled objects. For coordinates (θ_(c),φ_(c)) ofthe WorldCursor and coordinates (θ_(i),φ_(i)) of the center of a givenobject, the user is deemed to be pointing at a modeled object if:

√{square root over ((θ_(i)−θ_(c))²+(φ_(i)−φ_(c))²)}{square root over((θ_(i)−θ_(c))²+(φ_(i)−φ_(c))²)}<r_(i)  (1)

where radius r_(i) indicates the size of the object modeled as a circlein spherical coordinates. It is noted that this method of determining ifthe user is pointing at a modeled object in the environment is clearlymuch easier than the previously-described Gaussian blob technique usedin connection with the standalone XWand system.

In some cases the object being modeled in the environment will be betterrepresented as a polygon rather than a circle. In addition, in somecases the WorldCursor may be needed to indicate one or more points on anobject with a high degree of precision. Both of these issues areresolved by modeling the object in question as a polygon. This isaccomplished by inputting a set of vertices that form a polygonal modelof an object. To input the vertices, the user places the laser spot ofthe WorldCursor on each vertex of the polygon representing the object,in turn, while the WorldCursor system is in a training mode. Once theobject is “trained”, the system can then determine if the cursor is onthe polygon by using standard point-in-polygon algorithms used in twodimensional graphics [1].

More particularly, a model of a polygonal object in the space that theWorldCursor system is operating in can be established as follows.Referring to FIGS. 5A and B, the user initiates the aforementionedtraining mode that is part of an control process running on the hostcomputer, except also indicating a polygonal object is being modeled(process action 500). The user directs the laser by pointing the XWandso that the laser spot appears one of the vertices of the object beingmodeled and presses the button on the XWand (process action 502). Theprocedure then proceeds as before with the control process causingperiodic requests to be sent to the XWand directing it to provide anorientation message in the manner described previously (process action504). Any incoming orientation message transmitted by the pointer isinput (process action 506), and it is determined whether the buttonstate indicator included in the message indicates that the pointer'sbutton is activated (process action 508). If not, process actions 506and 508 are repeated. When it is discovered that the button stateindicator indicates the button is activated, the process associates thespherical coordinates of the target location to the object vertex beingmodeled (process action 510). Any incoming orientation messagetransmitted by the pointer continues to be input (process action 512)and a determination is made as to whether the button state indicatorincluded in the messages first indicates that the pointer's buttonbecomes deactivated and then activated again, thereby indicating thatthe user has pushed the XWand button again (process action 514). If itis, process actions 512 and 514 are repeated. If it is not, in processaction 518, it is determined if the last vertex has been identified bythe user (process action 516). If so the process ends. If not, processactions 502 through 518 are repeated to “learn” the next vertex of thepolygon. Optionally, either before or after the user points out all thevertices of the polygon being established to the model the object ofinterest, he or she can enter information into the host computer thatidentifies the object. This information would be associated with theobject as well.

Once an object has been modeled as a polygon, it might also be desirableto know precisely where the cursor (i.e., laser spot) is on the object'ssurface in a local coordinate system, as mentioned above. For example,this polygon technique can be used to determine if the WorldCursor spotis on the active surface of a computer display, and if so where on thatsurface. In this way the WorldCursor can act as a display cursor aswell.

For a four vertex polygonal surface such as a computer display, thedesired location would be the cursor's screen coordinates. A transformfrom WorldCursor to screen coordinates allows the display to beseamlessly incorporated into the rest of the world model, as describedlater. In this case, a projective transform [3] can be used to transformWorldCursor coordinates to screen coordinates (x, y) as follows:

$\begin{matrix}{\begin{bmatrix}{wx} \\{wy} \\w\end{bmatrix} = {\begin{bmatrix}p_{11} & p_{12} & p_{13} \\p_{21} & p_{22} & p_{23} \\p_{31} & p_{32} & 1\end{bmatrix}\begin{bmatrix}\theta_{c} \\\varphi_{c} \\1\end{bmatrix}}} & (2)\end{matrix}$

The parameters p_(ij) are determined by solving a linear system ofequations given the four corners of the display in both WorldCursor andscreen coordinates. Here the assumption is made that the WorldCursorcoordinate system is linear in the region of the display, even thoughmodeled in spherical coordinates—a valid assumption for typical sizeddisplays.

More particularly, the projective transform of Eq. (2) takes coordinates(x,y) into coordinates (x′,y′) by way of a 3×3 matrix with 8 freeparameters. Points (x_(i),y_(i)) are the coordinates of the 4 corners ofthe polygon in WorldCursor device coordinates, and the points(x′_(i),y′_(i)) are the coordinates of the same 4 corners in localcoordinates (e.g., screen coordinates of a computer display). Thesevalues are collected in an offline training procedure in which thecursor is placed on each of the 4 corners of the polygon in turn, asdescribed previously.

The matrix may be expressed as

$\begin{matrix}{{x^{\prime} = \frac{{p_{11}x} + {p_{12}y} + p_{13}}{{p_{31}x} + {p_{32}y} + 1}},{y^{\prime} = {\frac{{p_{21}x} + {p_{22}y} + p_{23}}{{p_{31}x} + {p_{32}y} + 1}.}}} & (3)\end{matrix}$

Rearranging terms gives:

x′=p ₁₁ x+p ₁₂ y+p ₁₃ −p ₃₁ xx′−p ₃₂ yx′

y′=p ₂₁ x+p ₂₂ y+p ₂₃ −p ₃₁ xy′−p ₃₂ yy′  (4)

From this linear system it is possible to solve for parameters p_(ij)given 4 points (x_(i),y_(i)) which map to corresponding points(x′_(i),y′_(i)):

$\begin{matrix}{\begin{bmatrix}x_{1}^{\prime} \\y_{1}^{\prime} \\x_{2}^{\prime} \\y_{2}^{\prime} \\x_{3}^{\prime} \\y_{3}^{\prime} \\x_{4}^{\prime} \\y_{4}^{\prime}\end{bmatrix} = {\begin{bmatrix}x_{1} & y_{1} & 1 & 0 & 0 & 0 & {{- x_{1}^{\prime}}x_{1}} & {{- x_{1}^{\prime}}y_{1}} \\0 & 0 & 0 & x_{1} & y_{1} & 1 & {{- y_{1}^{\prime}}x_{1}} & {{- y_{1}^{\prime}}y_{1}} \\x_{2} & y_{2} & 1 & 0 & 0 & 0 & {{- x_{2}^{\prime}}x_{2}} & {{- x_{2}^{\prime}}y_{2}} \\0 & 0 & 0 & x_{2} & y_{2} & 1 & {{- y_{2}^{\prime}}x_{2}} & {{- y_{2}^{\prime}}y_{2}} \\x_{3} & y_{3} & 1 & 0 & 0 & 0 & {{- x_{3}^{\prime}}x_{3}} & {{- x_{3}^{\prime}}y_{3}} \\0 & 0 & 0 & x_{3} & y_{3} & 1 & {{- y_{3}^{\prime}}x_{3}} & {{- y_{3}^{\prime}}y_{3}} \\x_{4} & y_{4} & 1 & 0 & 0 & 0 & {{- x_{4}^{\prime}}x_{4}} & {{- x_{4}^{\prime}}y_{4}} \\0 & 0 & 0 & x_{4} & y_{4} & 1 & {{- y_{4}^{\prime}}x_{4}} & {{- y_{4}^{\prime}}y_{4}}\end{bmatrix}\begin{bmatrix}p_{11} \\p_{12} \\p_{13} \\p_{21} \\p_{22} \\p_{23} \\p_{31} \\p_{32}\end{bmatrix}}} & (5)\end{matrix}$

During runtime, screen coordinates are computed from WorldCursor devicecoordinates using equation (2) above. Note that this computation is onlyperformed after it is determined that the cursor is contained within thepolygon described by the points (x_(i),y_(i)). Alternatively, one mayalways perform this mapping, and then check if the resulting screencoordinate values are contained within the polygon described by thepoints (x′_(i),y′_(i)) (a trivial calculation).

3.3 Controlling the WorldCursor System

In this section, various techniques for controlling the WorldCursor withthe XWand are presented. The general scheme of the control mapping isthat the WorldCursor should mimic the exact motion of the XWand, much inthe same way that the cursor on a WIMP interface mimics the motion ofthe mouse. If (θ_(c),φ_(c)) is the yaw and pitch of the WorldCursor and(θ_(w),φ_(w)) is the yaw and pitch of the XWand, then(θ_(c),φ_(c))≈(θ_(w),φ_(w)), at least for an absolute pointing mode aswill be described shortly.

3.3.1 Filtering

Before passing on the output of the XWand to the WorldCursor controller,the yaw and pitch values from the XWand are first filtered to reduce theeffects of noise in the sensors and to ease placing the cursor preciselyon a small target.

Two filters are used which average the last n samples (i.e., a boxfilter). The first is a very slow filter. For example, in testedversions of the WorldCursor, this slow filter averaged approximately thelast 2.5 seconds worth of sensor data. This filter tends to dampen mostXWand motion and allows the user to move the cursor relatively slowlyfor precise positioning. The second filter is much faster. For example,in tested versions of the WorldCursor, this fast filter averagedapproximately the last 0.3 seconds worth of sensor data. This fastfilter is appropriate for fast XWand movement, when the sensor noise isnot as apparent, and responsiveness is desired.

While the user could switch between the filter modes manually via inputto the host computer, the WorldCursor control process running on thatcomputer preferably switches between the slow and fast filtersautomatically. This is accomplished as follows. Referring to FIG. 6, andpresuming that the fast filter is the initial default selection, it isfirst determined if the average speed of the cursor movement has fallenbelow a prescribed slow speed threshold τ_(slow) (process action 600).If not, then the speed of the cursor continues to be monitored byperiodically repeating process action 600. It is noted that the speed ofthe cursor is determined by taking the estimated position returned bythe fast filter, and computing the difference between that estimate andthe same estimate computed in the previous time step, to get speed. Inaddition, the speed can be checked at any appropriate interval thatensures the cursor behaves in the aforementioned controlled manner. Intested embodiments of the control process, the speed was checked everytime step (e,g., about 50 Hz). If it is determined in process action 600that the cursor speed has fallen below the prescribed slow speedthreshold, then in process action 602 the WorldCursor control processswitches to the aforementioned slow filter. The cursor speed is thenmonitored again. More particularly, it is determined if the averagespeed of the cursor movement goes above a prescribed fast speedthreshold τ_(fast) (process action 604). If not, then the speed of thecursor continues to be monitored by periodically repeating processaction 604 in the manner employed previously. In general, the fast speedthreshold τ_(fast) is much higher than the slow speed threshold. Thisprevents frequent shifts and ensures a smooth transition between filtermodes at the appropriate times. While other values can be employed asdesired, in tested embodiments of the control process τ_(slow) was setto 0.05 radians/second and τ_(fast) was set to 0.5 radians/second. If itis determined in process action 604 that the cursor speed has risenabove the prescribed fast speed threshold, then in process action 606the WorldCursor control process switches to the aforementioned fastfilter. At this point, the filter selection procedure continues byrepeating actions 600 through 606, for as long as the WorldCursor systemis activated. In this way, a balance of speed, responsiveness and a finedegree of control are maintained.

3.3.2 Absolute vs. Relative Pointing

In the absolute pointing mode, the WorldCursor's laser ideally points atthe same place as the XWand. The most basic control mapping to computeWorldCursor yaw and pitch (θ_(c),φ_(c)) from the XWand yaw and pitch(θ_(w),φ_(w)) to produce this absolute pointing is,

θ_(c)=θ_(c0)+θ_(w)−θ_(w0)  (6)

φ_(c)=φ_(c0)+φ_(w)−φ_(w0)  (7)

where (θ_(c0),φ_(c0)) and (θ_(w0),φ_(w0)) are offset angles for theWorldCursor and XWand, respectively. These offsets are set to align theorigins of the XWand and WorldCursor in a one time calibrationprocedure.

However, unless the WorldCursor platform and the XWand are very close toone another, it will be impossible to choose offsets (θ_(c0),φ_(c0)) and(θ_(w0),φ_(w0)) such that the XWand points directly at the WorldCursorlaser spot throughout the range of pointing in the room. It will bepossible to achieve approximate correspondence for a limited range ofangles such as one wall of a room, but as soon as the WorldCursor isbrought onto the opposite facing wall, for example, the correspondencewill be far off.

It is not clear if users require even approximate correspondence forsuccessful use of the device. Users' experience with mice suggests thatabsolute correspondence is not necessary. Much in the same way thatusers easily adapt to the relative movement of mouse and cursor, usersof the WorldCursor may be able to adapt to the lack of absolutepointing, subject to the limitation that the laser spot is in theirfield of view. Thus, a relative pointing mode where the WorldCursor'slaser spot moves with the movement of the XWand, but does not point atthe same place in the environment, may be an acceptable operatingcondition. However, a number of procedures can be employed by which theWorldCursor and XWand can be brought into alignment to at leastpartially restore absolute pointing, and obtain other useful informationabout the environment as well. These alignment procedures will now bedescribed in the section below.

3.3.2.1 Clutching

One procedure that the user can employ to re-establish theXWand-WorldCursor correspondence involves a “clutching” technique. Thisis an operation analogous to picking up a computer mouse, moving it inair, and putting the mouse down on the desk again, without the cursormoving. To clutch, the user clicks the XWand button while theWorldCursor control process is in operational mode (as opposed totraining mode). At that point the laser dot stops moving with the XWand.The user may then reorient the XWand, lining it up so that it pointsdirectly at the laser spot. When ready to resume WorldCursor operation,the user clicks the button again and the laser spot resumes moving. Atthis moment new offset values (θ_(c0),φ_(c0)) and (θ_(w0),φ_(w0)) arealso collected.

More particularly, referring to FIGS. 7A and B, the user initiates theoperational mode of the WorldCursor control process, if it is notalready active (process action 700). In the operational mode, thecontrol process normally accepts XWand pitch and yaw inputs, computesthe corresponding pitch and yaw for the WorldCursor laser, and sendscommands to the WorldCursor unit to move the laser to match the computedpitch and yaw values, all in the manner described previously. Thisnormal operation continues until the user presses the XWand button toinitiate the clutching operation (process action 702). Specifically, thecontrol process causes periodic requests to be sent to the XWanddirecting it to provide an orientation message (process action 704), andany incoming orientation message is input (process action 706). Theseorientation messages include the aforementioned XWand pitch and yawvalues that are used to move the laser. They also include the XWandbutton state indicator. Thus, when a message is received it determinedwhether the button indicator indicates that the pointer's button isactivated (process action 708). If not, normal operations are continuedand process actions 706 and 708 are repeated. However, if it isdiscovered that the button state indicator indicates the button has beenactivated, then in process action 710, the control process ceasesproviding movement commands to the WorldCursor device and the laser spotremains stationary in its last position. The user then points the XWandat the location where the laser spot is shining (process action 714) andreleases the button. Any incoming orientation message transmitted by theXWand continues to be input (process action 712) and a determination ismade as to whether the button state indicator included in the messagesfirst indicates that the pointer's button becomes deactivated and thenactivated again, thereby indicating that the user has pushed the XWandbutton again (process action 716). If it has not, process actions 712and 716 are repeated. However, if it has, new offset values for theWorldCursor device and the XWand are collected (process action 718) andnormal operations are resumed (process action 720).

Note that the user may use the foregoing clutching technique not toalign the XWand with the WorldCursor, but to establish a particulardesired range of operation for the XWand. For example, by clutching theuser may set offsets so that the XWand may be held comfortably at theside of the body while the WorldCursor appears on a surface in front ofthe user. The procedure is the same except that the user does not pointthe XWand at the laser spot, but instead orients it as desired. Thisoption put the WorldCursor system into a relative pointing mode asexplained above.

3.3.2.2 Exploiting Room Geometry To Automatically Re-establishCorrespondence

Another procedure that the user can employ to establish and maintain areasonable correspondence between the XWand and WorldCursor withoutclutching involves exploiting the geometry of a room in which theWorldCursor system is operating. If the geometry of the room is known interms of a 3D coordinate system, including the position of each wall,the WorldCursor device, and the XWand itself, then the WorldCursor maybe controlled such that the XWand always points directly at the laserspot.

More particularly, if the 3D coordinates of the vertices of the walls inthe room are known, and the 3D position and orientation of the XWand arealso known, it is possible to compute the precise point on the wall thatthe XWand is pointing toward using standard polygonal analysistechniques. Then, using simple trigonometry (i.e., right triangleanalysis in both the yaw and pitch planes), this 3-D ‘wall point’ canthen be related back to the known 3D position of the WorldCursor deviceto compute an updated value of the yaw and pitch (θ_(c),φ_(c)) that isused to point the laser at the aforementioned point on the wall.

By relying on the three dimensional position of the XWand, it may seemlike the very same problem that it is desired to remove in developingthe WorldCursor is being re-introduced—namely the XWand's reliance onexternal 3-D positioning technology. In practice, however, it issufficient to know the room geometry only approximately and stillachieve a useable alignment that requires no clutching. For example, itwill typically suffice to fix the assumed XWand position in the middleof a typical office space, even though this may not coincide with itsactual position. Of course, such an assumption may not provide anaccurate alignment of the XWand and WorldCursor. However, in situationswhere relative pointing is acceptable this assumption can be made.Further other assumed XWand locations could be used instead to make thealignment more accurate. This is particularly useful when it is believedthat the XWand will be at or near a particular position most of the time(e.g., the room occupant's desk). Again, this relies on the fact thatusers tend to be tolerant to constant offsets in alignment similar tothat found in using relative pointing mechanisms such as computer mice.

3.3.2.3 Inferring 3D XWand Position To Re-establish Correspondence

A more accurate variation of the foregoing room geometry exploitationtechnique that can produce near absolute pointing results involvescombining the geometry exploitation technique with the clutchingprocedure to determine the 3D location of the XWand in the room. If theuser is clutching as described previously so that the XWand points atthe laser spot, each clutching operation provides information that canbe related mathematically to the 3D position of the XWand. After as fewas two clutching operations, it is possible to compute the 3D positionof the XWand.

More particularly, for each clutching operation performed with theWorldCursor laser spot shining on one of the walls whose verticescoordinates are known, there is an associated wall point p_(i), as wellas a vector w_(i) that defines a ray pointing from the XWand to the wallpoint. These values are collected at the end of the clutching operation,after the user has realigned the XWand with the laser spot of theWorldCursor and pressed the XWand button to resume WorldCursor control.Essentially, the wall point p_(i) can be computed via standard polygonalanalysis techniques since the 3D coordinates of the vertices of thewalls in the room are known, as are the 3D position of the WorldCursorbase and orientation of its laser (i.e., the direction the laser ispointing from the base). The vector w_(i) is defined by the orientationof the XWand that is determined as described previously. Assuming theXWand position x is held constant over a number of successive clutchingoperations, then

x+s _(i) w _(i) =p _(i)  (8)

where s_(i) is a scalar. It is noted that the “wall points” can actuallybe any point on any surface in the space that is modeled as a polygonvia the procedure described previously.

XWand position x can be found by solving the linear system of equationsgenerated via successive clutching operations using a standard leastsquares approach. A minimum of two clutching operations are required,but for robustness it is be desirable to collect several, particularlyif some of the rays w_(i) are similar, in which case the solution willbe sensitive to small errors in w_(i).

Once the estimate of the XWand position has been updated, the controlprocedure described in Section 3.3.2.2 is used to maintainXWand-WorldCursor correspondence. So long as the actual position of theXWand does not change dramatically, no more clutching operations will benecessary to maintain the correspondence. It is noted that this onlinecalibration requires no more clutching operations than the system whichdoes not exploit the approximate room geometry, and in the long runrequires fewer clutching operations if the user does not move about theroom often. The user would only be aware of the procedure in that aftera while no more clutching operations would be required to keep thecursor and the wand in alignment.

Accordingly, referring to FIG. 8, the XWand-WorldCursor correspondencecan be maintained by first determining if a clutching procedure beenperformed (process action 800). If a clutching operation was notperformed, action 800 is periodically repeated. However, if a clutchingoperation was performed, the 3D location of the point on the wall wherethe WorldCursor laser spot was shining during the clutching operation iscomputed (process action 802). In addition, the vector defining a raypointing from the XWand to the same point on the wall is computed(process action 804). It is next determined if a prescribed number ofclutching procedures have been performed (process action 806). If not,process actions 800 through 806 are repeated. If the prescribed numberis met, then the 3D position of the XWand is computed (process action808). Next, the point on the wall that the XWand is directed toward asit pointed around the space is periodically computed, as is the yaw andpitch values that will direct the WorldCursor laser at that point(process action 810). The WorldCursor laser is directed with these yawand pitch values whenever they are computed (process action 812).Finally, the entire process (i.e., process actions 800 through 812) isrepeated for a long as the WorldCursor is in operation.

It is noted that the number of clutching operations that must beperformed before the XWand-WorldCursor correspondence is updated canalternately be determined based on how different each of theaforementioned rays w_(i) are to each other, rather than using anabsolute number. For example, in one method, if the latest ray to becomputed does not differ from the previous rays computed since the lastcorrespondence update by a prescribed threshold difference, then it isnot counted in terms of how many clutching operations are required. Inthis way, any errors in the computation of the rays will not have asignificant impact on the overall correspondence computations.

It should be noted that some assumptions are made in regard to theforegoing procedures for establishing and maintaining theXWand-WorldCursor correspondence. For example, it is assumed that theuser is clutching to re-establish XWand and WorldCursor correspondence,and not to create a relative pointing relationship between them. Inaddition, it is assumed that the user in not moving about the room, butinstead remains in the same location. It is noted, however, that mostusers are likely to use the XWand from one a small set of staticlocations, much as the TV remote control is likely to be used fromeither the couch or the easy chair. Accordingly, this assumption isquite valid.

3.4 Establishing A 3D Model Of The Space Using The WorldCursor

In the foregoing procedures, it was assumed a polygonal model of thespace was available. However, if this is not the case, it is possible toconstruct one given that the positions of the XWand and WorldCursordevices are known. More particularly, given the 3D location of XWand andits orientation (i.e., the direction it is pointing) in combination withthe 3D location of the WorldCursor (which in this coordinate systemcould be designated as the origin if desired) and its orientation (whichis assumed to be directed at the same point as the XWand via theaforementioned clutching operation), then, it is possible to solve forunknown wall points p_(i) using simple trigonometry. Specifically, atriangle is formed by the 3D position of the XWand, the 3D position ofthe Worldcursor device, and the unknown wall point p_(i). Since the 3Dposition of the XWand and the 3D position of the Worldcursor device areknown, the distance between them can be computed. In addition, since theorientation of the XWand and the laser beam are known, it follows thattwo of the angles of the aforementioned triangle are also known. Thus,the wall point p_(i) can be uniquely determined using standardtrigonometric methods. In this way the 3D position of objects anddevices in the room may be learned, much as in the original XWandsystem. For example, the user while holding the XWand in substantiallythe same location within the space would point it at an object (e.g., atits center) or to the vertices of a polygon representing an object ofinterest in the space (including the walls) to establish their 3Dlocation and then enter information about the object, similar to thepreviously described procedure for establishing a model of the space interms of spherical coordinates.

Thus, with a sufficient number of clutching operations to maintain theXWand-WorldCursor correspondence intact, it would be possible to learnthe entire room geometry, including a polygonal model of the walls(which could then be used to thereafter run the foregoing procedures formaintaining the XWand-WorldCursor correspondence more automatically).However, it should be noted that even in this scenario, no moreclutching operations would be necessary than in the case of not using ageometric model.

The foregoing procedure for learning geometry from clutching operationsraises some interesting possibilities for inferring geometry over thenormal use of the device, without relying on a special training mode ora lengthy upfront training session. This has interesting implicationsfor ubiquitous computing applications, many of which rely on geometricmodels to develop location based services, and to reason about userco-presence and proximity to devices. One significant barrier todeploying such systems will be the construction of the necessarygeometric models, especially in the home. The foregoing feature of theWorldCursor system can provide a solution for this problem.

4.0 Applications 4.1 Home Automation

The WorldCursor system is capable of performing all the homeautomation-related tasks of the original XWand system, including turningon and off lights via X10 (i.e., a powerline-based home automationsystem), selecting and manipulating the media player with gestures tocontrol track and volume, and finally selecting and controlling a cursoron a display.

The WorldCursor improves on the XWand system by giving the user muchmore precision in selecting devices. In the original XWand system, forexample, it would be difficult without audio feedback to select one oftwo devices that are located 18 inches apart from 12 feet away. This isdue not only to the limited precision of the XWand system, but also inusers' limited precision in pointing. This uncertainty can be addressedby placing a laser pointer (always on) on the XWand itself, but only upto the precision of the XWand signal processing algorithms.

The WorldCursor precision can be exploited in one application where tocontrol the media player, the user puts the WorldCursor on one ofseveral paper icons (play, pause, next track, previous track) hung onthe wall. The user “presses” the media player button by pushing theXWand button. Menus and other traditional GUI metaphors may also beused.

4.2 Display Surfaces

In the original XWand system, the user may control a cursor on a consoleby first pointing the XWand at the console, and entering a cursorcontrol mode by clicking the XWand button. Exiting the cursor controlmode is accomplished by clicking on a special button presented in theinterface during cursor control mode.

With the precision afforded by the WorldCursor, it is possible toimprove upon this interaction by seamlessly integrating the displaysurface in the world model, without needing to enter a special cursorcontrol mode. For example, once the four corners of the display arespecified with the WorldCursor, the calculations described in Section3.2 may be used to determine if the cursor is on the display. If thecursor is on the display, the laser is turned off, and the prospectiveprojection equations are used to move the cursor to the exact spot onthe display where the laser would be if it had not been turned off. Oncethe user moves the cursor off the display, the cursor is hidden and thelaser is turned back on. Because of the nature of the WorldCursorgeometric model, the registration between the two coordinate systems canbe quite precise.

Further, with networked WorldCursor client processes it will be possibleto extend this functionality across multiple displays simultaneously,moving from display to display seamlessly.

The drawback of the WorldCursor display integration is that the controlof a small display from across the room can be quite difficult, sincethe size of the ‘mousing surface’ is related to the angle subtended bythe display. In the XWand system, this problem is avoided in the specialcursor control mode by using a constant scaled range of angles forcontrol that is independent of where the user is located in the room.One approach to address this limitation is to nonlinearly warp thecoordinate system in the neighborhood of the display.

4.3 Learning Geometric Models

Besides using the WorldCursor to ‘point out’ devices to the system, itmay also be used by the system to ‘point out’ devices to the user. Forexample, if the intelligent environment knew where the user's lost keyswere, the WorldCursor system might direct the user's attention to theirlocation in response to the user's query.

4.4 Non-Veridical Behavior

Thus far WorldCursor control and applications which strive to replicatethe exact motions of the user's manipulations of the XWand have beenexplored. There may also be interesting possibilities in considering howthis one to one mapping may be violated.

For example, in [2] users' ability to finely control a standard laserpointer in an object selection task is studied. In part, performingobject selection and other GUI related tasks with a laser pointer isdifficult because it is surprisingly difficult to hold a laser pointerstill. In Section 3.3.1, a switching filter technique was describedwhich can be used to significantly dampen the motion of the cursor whenthe user is moving the XWand slowly. The WorldCursor can thus do forlaser pointer-based interaction what ‘SteadyCam’ has done for homevideos, by eliminating the jitter and noise associated with standardlaser pointers. This damping filter is especially useful in working withdisplay surfaces, where often GUI elements are small and densely packed.Thus, the WorldCursor system can act as an improved laser pointer.

In an environment where there are many selectable objects, it may beadvantageous to employ a “Snap To” feature for the WorldCursor. If theuser guides the cursor near an active device, a simple spring model maybe used to bring the cursor precisely on the target. For example, asimple distance threshold can be employed such that if the laser beam ismoved to a location near an object that is within the thresholddistance, it is automatically redirected to the shine on that object.Not only may this ease target selection, it also is a convenient way toalert the user to the fact that the object is active and selectable.

In the case when the XWand is used with gestures to control thecurrently selected device, the WorldCursor can be used to ‘play back’the gesture as a way to teach the user the available gestures for thatdevice.

As with the mouse, users of the WorldCursor attend the cursor and almostnever look at the XWand itself. In some cases users have difficultyfinding the laser spot, particularly in the case when the cursor is‘parked’ at a location in the environment out of the field of view, asin the beginning of a clutching operation. One solution to this problemis to bring the cursor to a ‘home’ position after a period ofinactivity, or to animate the laser spot to draw the user's attentionwhen the XWand is first picked up.

While throughout the foregoing description of the WorldCursor system theXWand was employed as a pointing device, this need not be the case.Generally, any conventional pointing device could be used to steer theWorldCursor laser. For example, a computer mouse, track ball, or gamepadcould be adapted to this purpose. Of course, some of the above-describedfeatures of the XWand-WorldCursor combination would not be possible,such as the absolute pointing mode and 3D modeling features, because ofthe lack of pointer orientation data. However, the conventional pointingdevices can support features such as spherical coordinate modeling andobject selection, the above-described display surface feature, andgeneral laser pointer-type functions.

5.0. References

-   [1] Haines, E. (1994) In Graphics Gems IV (Ed, Heckbert, P.)    Academic Press, pp. 24-46.-   [2] Myers, B. A., R. Bhatnagar, J. Nichols, C. H. Peck, D. Kong, R.    Miller, and A. C. Long (2002), Interacting At a Distance: Measuring    the Performance of Laser Pointers and Other Devices, in Proceedings    CHI Minneapolis, Minn.-   [3] Zisserman, H. R. a. A. (2000) Multiple View Geometry in Computer    Vision, Cambridge University Press.

1. A system comprising: an object position determination deviceconfigured to determine a first position of an object at a first timeand a second position of the object at a second time, the objectposition determination device including a camera configured to detectlight traveling from the object to the camera; and an inputdetermination device configured to determine an input based at leastpartly upon the first position and the second position, the inputcorresponding to one of a plurality of stored gestures.
 2. The system ofclaim 1, wherein the object position determination device includes asecond camera.
 3. The system of claim 2, wherein at least one of thecamera and the second camera is an infra red camera.
 4. The system ofclaim 1, wherein the object includes an infrared emitter.
 5. The systemof claim 1, wherein the object is an electronic device.
 6. The system ofclaim 1, further comprising: a training device configured to obtaintraining data from a user, wherein the input determination device isfurther configured to determine the input based at least partly upon thetraining data.
 7. A method comprising: detecting, by a camera, firstlight traveling from an object to the camera at a first time;determining a first position of the object at the first time based atleast partly on the first light; detecting, by the camera, second lighttraveling from the object to the camera at a second time; determining asecond position of the object at the second time based at least partlyon the second light; and determining an input based at least partly uponthe first position and the second position, the input corresponding toone of a plurality of stored gestures.
 8. The method of claim 7, furthercomprising: detecting, by a second camera, third light traveling fromthe object to the second camera at the first time; determining the firstposition of the object at the first time based at least partly on thethird light; detecting, by the second camera, fourth light travelingfrom the object to the second camera at the second time; and determiningthe second position of the object at the second time based at leastpartly on the fourth light.
 9. The method of claim 8, wherein at leastone of that camera and the second camera is an infra red camera.
 10. Themethod of claim 7, wherein the object includes an infrared emitter. 11.The method of claim 7, wherein the object is an electronic device. 12.The method of claim 7, further comprising: obtaining training data froma user; and determining the input based at least partly upon thetraining data.
 13. A computer storage medium storing computer-executableinstructions that when executed by a processor cause a computer toexecute steps comprising: detecting first light traveling from an objectto a camera at a first time; determining a first position of the objectat the first time based at least partly on the first light; detectingsecond light traveling from the object to the camera at a second time;determining a second position of the object at the second time based atleast partly on the second light; and determining an input based atleast partly upon the first position and the second position, the inputcorresponding to one of a plurality of stored gestures.
 14. The computerstorage medium of claim 13, wherein the steps further comprise:detecting third light traveling from the object to a second camera atthe first time; determining the first position of the object at thefirst time based at least partly on the third light; detecting fourthlight traveling from the object to the second camera at the second time;and determining the second position of the object at the second timebased at least partly on the fourth light.
 15. The computer storagemedium of claim 14, wherein at least one of that camera and the secondcamera is an infra red camera.
 16. The computer storage medium of claim13, wherein the object includes an infrared emitter.
 17. The computerstorage medium of claim 13, wherein the object is an electronic device.18. The computer storage medium of claim 13, wherein the steps furthercomprise: obtaining training data from a user; and determining the inputbased at least partly upon the training data.